AC motor troubles with Lathe

D

Denzel

Senior Member
I know this forum is intended for Picaxe discussion primarily but I know many experienced members will have a lot of knowledge about metal lathes. I have just dug out my grandfathers Emco compact 8 metal Lathe and the AC motor (240vac 0.65kw) is having trouble getting going.

When I turn it on it hums and gets quite hot, but does not turn. Could their be a short somewhere? or are the brushes likely to be nacked? The reason I am confused is that if I give the cuck a bit of a spin with my hand it'l get going but at only about a 5th of the speed it should be.

Any ideas?

Cheers

Denz
 
M

moxhamj

New Member
If it turns but only slowly and only if you start it turning, it could be that one brush is worn but the other(s) are still ok. Though probably almost worn out too. I've had motors repaired and there are people who do this professionally. A lathe would be very useful and it if was just a matter of getting the motor going, it would be worth the money.
 
J

Jaguarjoe

Senior Member
Check the starting capacitor and/or the centrifugal switch. Either way, it sounds like its a problem with the start winding circuit.
 
W

westaust55

Moderator
As an AC motor it may not have brushes at all.

Often single phase motors have a start winding with a centrifugal switch to cut out the motor once it is spinning.
The start winding works with a capacitor in series with the start winding to give a phase shift for a simulated added magnetic pole within the motor to help pull the rotor around until it gets spinning.

As you indicate that it is running but at low speed if you give it a "flick", that might suggest that the start winding could be okay and that the main winding has failed.

The start winding is only intended to be powered for a short time and this could be the cause of the motor getting hot.
Alternatively there may be some shorted turns in the main winding.
 
D

Denzel

Senior Member
...

Thanks for the quick reply this is really helpful, It's a $2000 Lathe so it would be a great shame to let it rust away unused.

I have actually got it to start without a spin on the chuck first time once (at good speed), which doesn't really tell me much anyway, just that whatever is faulty is not completely gone, just on its way.

My inititial thoughts went to the starting capacitor, quick question, where is this located? in the AC motor capsule itself? or within the controls of the Lathe?

I will do a bit more reading in the spare parts guide I found with the device as to replacing the startup capacitor if this is the problem.

I will take the motor off when possible and give it a good inspection
 
K

kevrus

New Member
Capacitors are usually mounted on the motor casing or sometimes in/on the terminal block housing.

Some single phase motors have the capacitor permanently in circuit and no centrifugal switch, others can have one capacitor that is switched out by the centrifugal switch, others have two capacitors, a start and a run, the start bieng switched by the centrifugal switch as already mentioned and the run capacitor remaining in circuit.

This switch can often be heard to operate...a click quite soon after the motor starts and achieves a certain speed.
 
D

Denzel

Senior Member
...

Thanks Dippy thats just what I was after, had a look on that forum before coming here but didn't come across anything as perfect as what you've found:

Emco distributor: "He told me to put the motor into the machine, turn it on and spin the spindle by hand. If the spindle then carried on running, it would be the capacitor."

Thats the money shot right there,
Will take my motor off and replace the Cap, unless of course there are other obvious signs of damage/breakage when inspected.

I'll let you know how it goes.

Denz

[Edit] Just read further to find this did not solve the particular problem, however I will investigate
 
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Andrew Cowan

Senior Member
If you can't solve it, you can always buy a new motor. A new 500W motor can be had for around £70. Note that the box mounted ontop of the motor houses the starting capacitor. I have one of their 550W motors on my bandsaw, and it works really nicely.

A
 
D

Dippy

Moderator
Ah yes, you can always buy new... ;)
But will it fit?

My Bridgeport motor died a few years ago. Bloomin' rubbish, it was only 34 years old!
Options:
1. New Beijing Motor £400
2. New UK Motor £700
3. Rewound £150 (cash job).

Option 3 was taken. Worked poifectly.
But if the problem is a few quids worth of capacitor or something trivial then that is the first thing to look at. This could go on all day.
 
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